netdev - Re: [PATCH net-next 9/9] mptcp: refactor sndbuf auto-tuning

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Date: Mon, 06 Nov 2023 08:21:52 +0100
From: Paolo Abeni <pabeni@...hat.com>
To: Eric Dumazet <edumazet@...gle.com>, Mat Martineau <martineau@...nel.org>
Cc: Matthieu Baerts <matttbe@...nel.org>, "David S. Miller"
 <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>,
 netdev@...r.kernel.org,  mptcp@...ts.linux.dev
Subject: Re: [PATCH net-next 9/9] mptcp: refactor sndbuf auto-tuning

Hi,

On Thu, 2023-11-02 at 18:19 +0100, Eric Dumazet wrote:
> On Mon, Oct 23, 2023 at 10:45 PM Mat Martineau <martineau@...nel.org> wrote:
> > 
> > From: Paolo Abeni <pabeni@...hat.com>
> > 
> > The MPTCP protocol account for the data enqueued on all the subflows
> > to the main socket send buffer, while the send buffer auto-tuning
> > algorithm set the main socket send buffer size as the max size among
> > the subflows.
> > 
> > That causes bad performances when at least one subflow is sndbuf
> > limited, e.g. due to very high latency, as the MPTCP scheduler can't
> > even fill such buffer.
> > 
> > Change the send-buffer auto-tuning algorithm to compute the main socket
> > send buffer size as the sum of all the subflows buffer size.
> > 
> > Reviewed-by: Mat Martineau <martineau@...nel.org>
> > Signed-off-by: Paolo Abeni <pabeni@...hat.com>
> > Signed-off-by: Mat Martineau <martineau@...nel.org
> 
> ...
> 
> > diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c
> > index df208666fd19..2b43577f952e 100644
> > --- a/net/mptcp/subflow.c
> > +++ b/net/mptcp/subflow.c
> > @@ -421,6 +421,7 @@ static bool subflow_use_different_dport(struct mptcp_sock *msk, const struct soc
> > 
> >  void __mptcp_set_connected(struct sock *sk)
> >  {
> > +       __mptcp_propagate_sndbuf(sk, mptcp_sk(sk)->first);
> 
> ->first can be NULL here, according to syzbot.

I'm sorry for the latency on my side, I had a different kind of crash
to handle here.

Do you have a syzkaller report available? Or the call trace landing
here?

Thanks!

Paolo